Catalyst Studies of Supported Metal Sintering and Redispersion Kinetics

1 Sintering Problems and Their Importance in Catalysis. - Catalyst deactivation is an important, develq ing subdiscipline of catal c science. It concerns the scientific investigation catalyst deactivation processes and the modeling and/or prediction of deactiva- 

There are four principal ways in which catalysts undergo deactivation (1) poisoning, (2) fouling, (3) sintering, and (4) volatilization. Mechanistically these processes can be classified as chemical, mechanical, or thermal. These mechanisms of catalyst deactivation are described and discussed in detail in several recent reviews and books. This review focuses on some impOTtant scientific facets of one of these important mechanisms, namely sintering. 

Sintering is an important mode of deactivation in supported metals which find broad application as catalysts in automotive, chemical, gas, and petroleum industries. The high surface area support (carrier or substrate) in these catalysts serves several functions (1) to increase the dispersion and utilizaticm of the catalytic metal phase, (2) to separate rfiysically metal crystallites and to bind them to its surface, thereby enhancing their thermal stability toward agglomeration, and (3) in stxne cases to modify the catalytic properties of the metal and/or provide separate catalytic functions. The second function is key to the prevention or inhibition of thermal degradation of the catalytically active metal phase. 

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C.H. Bartholomew, "Model Catalyst Studies of Supported Metal Sintering and Redispersion Kinetics," Catalysis, Specialist Periodical Report, Royal Society of Chemistry, Thomas Graham House, Cambridge, UK, Vol. 10,1992,... 

Model Catalyst Studies of Supported Metal Sintering and Redispersion Kinetics ... 

Studies of sintering and redispersion of supported metal catalysts have been reviewed by several authors [M8] most of these reviews focus on early kinetic studies of sintering of supported metal catalysts using a simplified power law expression (SPLE). Unfortunately this crude approach does not permit sintering kinetics to be presented in a consistent way nor does it enable (1) useful extrapolation of the data to other conditions (2) useful quantitative comparisons between different studies, or (3) physically meaningful kinetic parameters to be obtained. The ultimate result has been confusion regarding the effects of reaction parameters such as atmosphere and temperature and of catalyst properties such as support promoters, etc., on sintering rates. 

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